Restaurants are opening, parks are full and people are getting back to work: parts of Europe, Asia and much of the Middle East are enjoying the benefits of flattened Covid-19 curves. Meanwhile, parts of the US, India and Latin America are still recording thousands of new cases every day.
The first wave of the Covid-19 is not over. The future shape of the pandemic will be decided both by human action, in the form of social distancing, testing and other traditional methods of disease control, but also several unanswered questions about the nature of the virus itself.
Experts say there are several possibilities.
Peaks and troughs
One is that the Covid-19 breaks out and is suppressed in peaks and troughs, until enough of the population is vaccinated or potentially develops immunity.
Antibody tests in most places indicate that quarantine measures were very effective in slowing down the virus. Fewer than 10% of populations in France, Spain and Sweden have developed the antibodies that would be evidence of having caught the virus and, in theory, becoming immune, for at least a short time.
But that also means the vast majority of populations remain susceptible.
If societies reopen before the virus is sufficiently eradicated, it may be that this first wave does not completely go away, says Angela Rasmussen, a virologist at Columbia University.
“In the US, we are lifting lockdowns when there are still increasing numbers of cases in a bunch of states … We may just have peaks and valleys of transmission occurring over and over again as peoples behaviour changes,” she says.
The scale of these peaks could be reduced by making changes such as wearing masks, using public transport in a staggered way and avoiding overcrowded social events – which are increasingly being blamed for being “super-spreaders” of the first wave of the coronavirus.
If outbreaks grow too large, some governments might choose to reimplement quarantines. “If were reopening and we start to see case numbers growing rapidly in a few weeks, we may see rolling lockdowns or shutdowns to try to control the virus in those areas,” Rasmussen says.
Most influenza pandemics have historically struck in distinct wave patterns, with a first peak usually followed by a resurgent second wave six months later. But there is no guarantee Sars-CoV-2 will play out in the same way.
Social distancing and robust testing – or a lack of it – will be critical in deciding the future of the pandemic. But its shape will also be influenced by factors outside our control.
The first is whether we can become immune to the virus, and if so, how long that protection endures for
Sometimes immunity can last for decades. During the 2009 swine flu pandemic, public health authorities were initially confused as to why many older people seemed to be immune. Later, they discovered the virus was structurally similar to one that circulated during the 1918 pandemic. The immune systems of many older people had dealt with a similar virus 92 years ago.
Resistance to some earlier discovered coronaviruses has been thought to fade within a year. If immunity to Sars-CoV-2 is not permanent, a report from Harvard epidemiologists says it is likely to enter into regular circulation, coming in annual or biennial waves or sporadic outbursts.
The frequency of significant outbreaks may also be influenced by the weather. Most influenzas spread more easily in the winter because the virus is thought to prefer dry air over humidity, and because people in cold environments spend more time indoors and close to each other.
Existing coronaviruses also follow seasonal patterns. If this coronavirus behaves in the same way – and there is not yet strong evidence that it does – we could see regular wintertime surges of Covid-19.
But with so many people still apparently not immune to the virus, that summer relief may not arrive this year, says James Hay, a postdoctoral research fellow at Harvards Chan School of Public Health.
“The factor that most contributes towards transmission is how many people are still susceptible,” he says. “And with so many still susceptible, thats going to swamp out any climate effect.”
Significant mutations in the virus might also lead to a wave of new infections down the track. So far, scientists say that isnt a huge concern.
“Even though there are different genomes out there that have changes compared to each other … theres no evidence any of those changes are in spots that are critical for the immune system to recognise,” Rasmussen says.
But that doesnt mean we wont see a significant mutation later. “Weve only known about this for six months, so its possible different strains could emerge in the future, because it does have a higher mutation rate,” she says. “But right now theres no evidence that thats happening.”
Infections are kept under control
For countries that are able to implement highly effective interventions such as testing and contact tracing, this first wave of coronavirus cases may be the last they experience, at least for some time.
In New Zealand, which has managed to virtually eradicate the virus and installed robust systems to monitor new outbreaks, there may be no significant new outbreaks or future waves at all, says Nick Wilson, a professor of public health at the University of Otago
“New Zealand is about to eliminate this virus,” Wilson says. “Even if there are border control failures, I expect that the contact tracing system is now good enough to control an occasional outbreak. So this country should be able to avoid future waves until a vaccine arrives.”
Countries with small populations and isolated geography such as New Zealand and Australia may be able to pull this off. South Korea is another country whose virus detection and suppression systems may be advanced enough to smother any future outbreaks. But it will be extremely difficult for most countries, especially those with large populations and porous borders.
The virus peters out
There are a minority of epidemiologists who argue the deadliness of the coronavirus has been overstated. One of the most prominent is Sunetra Gupta, a professor of theoretical epidemiology at Oxford University, who says the virus could already be on the way out.
She argues that the antibody studies conducted so far have been unreliable, and do not take into account the possibility that many people might already be immune to Covid-19 because of exposure to more benign coronaviruses.
Others, including neuroscientist Karl Friston, have also spoken of some populations such as Germanys having some kind of immunological “dark matter” that has kept fatalities there low compared to Spain, Italy or the UK.
This view is an outlier, and most governments have preferred to plan for the worst-case scenario – that millions of people are vulnerable to the virus. But Gupta argues the fact that virus transmission rates have peaked and fallen even in some places that did not institute harsh lockdowns is evidence for her theory.
“In almost every context weve seen the epidemic grow, turn around and die away – almost like clockwork,” Gupta told the media outlet UnHerd last week.
“To me that suggests that much of the driving force here was due to the buildup of immunity,” she says. “I think thats a more parsimonious explanation than one which requires in every country for lockdown, or various degrees of lockdown, including no lockdown, to have had the same effect.”